Graft ABS resins have become a predominant plastic in the engineering polymer field. They are made by emulsion, suspension, solution, and bulk techniques, or by a combination thereof. In 1976, over 2 billion pounds of ABS was made worldwide, a vast majority of this production being by the emulsion technique which requires induced coagulation of the polymer by the addition of inorganic salts or acids, washing, filtering and drying to produce a polymer in the form of powder.
Suspension polymerization of ABS is employed on a small scale but the product thus obtained is deficient in impact strength, thus limiting its use in many applications. Typical solution rubbers are employed in suspension ABS processes, and the amount of rubber that can be utilized is limited by its viscosity in the monomer solution. The suspension prepared ABS has the advantage, however, of being in bead form.
U.S. Pat. 3,436,440 recognizes the problem of recovering the ABS polymer from the emulsion and teaches the preparation of an ABS polymer made by suspension polymerizing acrylonitrile and styrene in the presence of a butadiene rubber in the form of an emulsion. However, it has been found that an ABS polymer made by first emulsion polymerizing acrylonitrile and styrene monomers in the presence of a butadiene rubber latex to form a high rubber graft latex; coagulating the thus formed latex; and then suspension polymerizing acrylonitrile and styrene in the presence of the coagulated emulsion results in a recoverable bead-like particle, which when fabricated, has greater impact resistance than when the monomers are suspension polymerized in the presence of the butadiene rubber emulsion, due to the fact higher rubber levels can be obtained by the present emulsion-suspension method.